Telephone-exchange switchboard apparatus.



PATENTED SEPT. 13, 1904.

F. R. MUBERTY.

TELEPHONE EXCHANGE SWITCHBOARD APPARATUS.

APPLICATION FILED JAN. 13, 1902.

N0 MODEL.

m. 1 N M W 1w mm A V ma k n W UNITED STATES Patented September 13, 1904.

ATENT OFFICE.

FRANK R. MCBERTY, OF EVANSTON, ILLINOIS, ASSIGNOR TO WVESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLIN 01S.-

TELEPHONE-EXCHANGE SWITCHBOARD APPARATUS.

SPECIFICATION forming part of Letters Patent No. 769,'? 60, dated September 13, 1904.

Application filed January 13, 1902. Serial No. 89,405. (No model.)

To all who? it lib/LI] concern:

Be it known that I, FRANK R. MOBERTY, a citizen of the United States, residing at Evanston, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Telephone-Exchange Switchboard Apparatus, of which the following is a full, clear, concise, and exact description.

My invention relates to the apparatus and circuits used by the operator at the central office of a telephone-exchange, and more particularly has to do with systems in which incandescent lamps are used in local circuits for indicating the call of the subscriber and the clearing-out signal.

Heretofore two lamps have been used in local circuits, one for indicating the call of the subscriber placed in connection with a local circuit connected with the thimble of the spring-jack switches and adapted to be lighted or caused to glow when the subscriber takes downhis telephone, the said local circuit being thus closed by a relay. The clearing-out signal or lamp has been included in one of the strands of the cords and adapted to be closed in parallel with the lamp constituting the linesignal when the plug is inserted. The two lamps thus included in parallel are adjusted with respect to the potential of the batterycircuit, so that when the two are thus connected in parallel neither will glow. Defect exists in this system, owing to the fact that when the operator inserts a plug in a switch of a line the tip of the plug may by chance touch the test-thimble, and on account of the connection of the tip-strand of the cord with that side of the cord-circuit battery which is connected to ground the normal resistance in circuit with said line -signal lamp will be shunted by such accidental touching of the tip against the test-thimble, so as to cause an abnormally great current to flow through the lamp, causing it to flash or glow brightly during the time of such contact. This current is sometimes sufficient to burn out the filament and destroy the lamp.

The object of my invention is to prevent such flashing of the lamps; and, speaking generally, my invention consists in connecting the tip of the plug with the circuits in such a way that if the tip should engage the testring of the jack the line-lamp will be merely shunted and in providing a normal break in the tip strand connected with the callingplug, combined with a relay for closing such break, the normal connection of the tip of the calling-plug being to the same side of the battery with which the test-thimbl'es of the jacks are normally connected through a highresistance winding of the induction-coil of operators telephone set.

I will now describe my system as illustrated in the accompanying drawing.

Two telephone-lines are illustrated, each extending in two limbs 1 Qfrom a substation to the central office. The usual telephonesubstation apparatus is shown. including a signal-bell and condenser in a bridge of the line and a telephone-receiver and transmitting apparatus in a second bridge controlled at the contacts of the usual gravity telephoneswitch. The circuit of the line is normally open, but is automatically closed by the telephone-switch when the receiver is taken from the hook for use.

The limbs 1 2 of the telephone-line are connected at the central oflice with the contactsprings (4 (4 respectively, of multiple springjacks a. A central battery 6, the positive pole whereof is grounded, is connected in the circuit of each line, and each line is provided with a line-relay 0, whose windings are included in the limbs 1 2, the relay being thus in the path of current from the central battery when the circuit of the line is closed at the substation. A line-signal lamp (Z is connected in a local circuit Ito ground from the free pole of the central battery 6, which is controlled at the contacts of the line-relay 0. This circuit at includes a resistance a between the lamp and ground. Each of the springjacks (a is provided with the usual third contact or test-ring a, and a conductor 3 extends from the test-rings of all the jacks of each line to earth through the resistance (2.

The operator is provided with a pair of plugs f g, united by link conductors of a cordcircuit, whereby any two lines may be connected together by inserting the plugs in the spring-jacks of such lines. Each plug is provided with the usual tip, ring, and sleeve contacts, which are adapted to engage, respectively, with the short and long line springs and the test-ring of the jack into which the plug may be inserted. The tip and ring contacts f f of the answering-plug f are connected with the corresponding tip and ring contacts g g of its mate or calling-plug g by conductors 5 6 of the plug-circuit, which include the windings of the usual repeating-coil. The central battery 5 is connected in a bridge of the plugcircuit between the windings of the repeating-coil, the connection being such that the groundedpole of the battery is connected with the ring strand 6 of the plug-circuit instead of with the tip-strand 5, as has been usual heretofore. Supervisory signal-lamps h h are provided for the plug-circuit included in conductors 7 7from the free pole of battery I) to the third contacts f g respectively, of the plugs. l Vhen the plug is inserted in the spring-jack of any line, therefore, the conductor 7 including the supervisory signal, which is associated with the plug in question is brought into parallel with the circuit-4, containing the line-signal lamp of the line whose circuit has been plugged, into.

An operators telephone set is illustrated in connection with the plug-circuit, and an operators listening-key 2' is provided, adapted to connect the operators telephone in a bridge of the cord-strands 5 6 between the central battery 6 and the answering-plug. The operators telephone set is provided with an induction-coil is, having three'windings. The primary winding k is included in a local circuit with a battery and a transmitter. The secondary winding 10 is included in circuit with the receiver and a condenser, the terminals of this circuit being connected with the springs of the listening-key, whereby this circuit may be included in a bridge of the plug-circuit. The tertiary winding 10 of the operators induction-coil, which is of high resistance, is normally connected with the tip g of the calling-plug through the armaturelever and back contact of a relay Z. The armature is connected with the tip of the callingplug, and a front contact is provided, against which the armature is adapted to strike when the relay is excited, this front contact being connected through one winding of the repeat ing-coil in the plug-circuit with the free pole of the battery 6. In other words, the relayl controls a normal break in the conductor 5 of the plug-circuit, the tip of the calling-plug being normally connected to earth from the tertiary of the operators induction-coil; butwhen the relay Z is excited the branch containing the tertiary winding k is cut off and the circuit 5 is completed between the central battery b and the tip of the calling-plug.

The winding of the relay Z is included in a branch conductor 8 between the free pole of the battery 6 and the third contact 9 of the calling-plug, so that this relay is excited when the calling-plug is inserted in the spring-jack of any line, the local circuit of said relay being made up of conductors 8 and 3, united in registering contacts of the plug and jack, and thence to earth through the resistance 6, which is associated with the line in question. order to etfectively shunt one lamp by another, the common resistance 6 must be relatively high. If the connection from the tip of the plug is to the same pole of the battery to which resistance a is connected, as is the case in systems of the prior art, then the tipstrand of the cord-circuit will constitute a shunt about resistance 6 when the tip engages the sleeve of the jack upon the insertion of the plug. If the resistance in this shuntingstrand of the cord-circuit be not high relative to the resistance 6, the current through the lamp or lamps, as the case may be, will be greatly increased. If it is highbeing one winding of the cord-circuit repeatingcoil the current-flow in the cord-circuit is cut down and transmission is impaired. By the use of my invention as thus described abnormal currents in the lamps are avoided without impairing transmission.

The operation of the system isas follows: When one subscriber of the exchange desires to communicate with another subscriber, he calls up the central office by removing his telephone from its hook, thereby closing his lines circuit and so bringing about the excitation of his line-relay c. The local circuit 4:, in-. cluding the line-signal lamp d of his line, is thus closed and the line-lamp lighted to indicate to the central-oflice operator that connection is desired. The operator responds to this signal by inserting her answering-plugf in the answering-jack of the line in question and by depressing her listening-key brings her telephone into the circuit of the callingline and inquires the number of the subscriber wanted. When the answering-plug is inserted, the conductor 7 is united with the conductor 3, whereby the supervisory signallamp in is brought into parallel with the linelamp (Z.

IIO

The two lamps and the resistance 6 are so adjusted relatively to the battery 6 ing learned the number of the subscriber wanted, the operator picks up the callingplug g in order to insert it in the springjack of that line and complete the connection; but in order that she may not make connection with a line which is already connected at some other section of the multiple switchboard she makes a preliminary test to find out whether or not the wanted line is free. This test consists in touching the tip 9 of the call ing-plug to the ring contact or thimble a of the spring-jack of the line and listening in her telephone. If the line in question is free, there will be no difl'erence of potential between the tip of the plug and the thimble of the jack to which it is touched and no noise will be heard in the telephone; but if a connection already exists at some other of the multiple spring-jacks of the line all the thirnbles a of that line will be connected with the battery 7), so that there will be a difference of potential between the thimble of the jack and the tip of the plug with which the test is made. As the tip of the plug touches the thimble, therefore, the current will flow to earth through the tertiary winding k of the operators induction-coil, which will cause a click in the operators receiving-telephone, thereby warning her that the line tested is busy. If upon testing the line wanted it is found to be free, the operator completes the connection by inserting the calling-plug clear in the jack of the line wanted and transmits a call-signal in the usual way. It is understood, of course, that the plug-circuit may be provided with the usual ringing-key for connecting a source of calling-current with the callingplug to ring the bell at the substation of the line with which such calling-plug may be connected. This ringing-key is not shown in the drawing, but is well known in the art. The insertion of the calling-plug in the spring-jack of the called line completes the local circuit, including the relay Z, so that the relay is excited and draws up its armature, cutting off the connection of the tip of the calling-plug with the operators induction-coil and connecting the same instead with the end of conductor 5 to complete the cord-circuit. The two subscribers lines are thus united for conversation. The signal-lamps associated with the united lines are not lighted, the linelamp of each line being in a closed shunt or branch about the supervisory lamp of the plug which is temporarily associated with the line. W'hen, however, either of the subscribers replaces his telephone on its switchhook, as at the termination of conversation, the line-relay of that subscriber will be deprived of current and will allow its armature to fall back, breaking the branch path which includes the line-lamp, and thus allowing increased current to flow through the supervisory lamp. The illumination of both supervisory lamps indicates to the operator that the conversation is finished and that both of the subscribers have hung up their telephones, and she takes this as a signal to disconnect the lines by pulling out the plugs.

The system above described differs structurally from systems of the prior art principally in two features.

First, in that the battery 1) is so connected with the plug-circuit that the strand terminating in the tip of the answering-plug is adapted to act as a shunt-circuit around the line-lamp of any line when the circuit through the line-signal of that line is closed, so that the line-lamp will not be flashed or receive an increase of current as the tip of the plug strikes the thimble of the jack while the plug is being inserted. in systems of this charac ter heretofore known the tip-strand of the cord-circuit has been connected with the grounded pole of the battery, and while a test was being made the resistance a would be shunted, and the currentfrom battery 5 would find a low-resistance path to earth through the line-signal lamp, the result being that the lamp would be momentarily flashed and in many instances would be burned out by the abnormal current.

Second, the change in the connection of the battery thus described would cause a false test if it were not for the second feature of my invention, which consists in providing in a system of the character described an electromagnetic switch or relay for keeping the tip of the calling-plug with which the test is made disconnected from the free pole of the battery until after the test. calling-plug were connected directly with the free pole of the battery 5 through the winding of the repeating-coil, the operator would hear a click in her telephone on touching the tip of the calling-plug to the test ring or thimble of the springjack of any line, whether such line were busy or not, since the tip of the plug would have its potential raised with relation to any of the thimbles; but in accordance with my invention 1 provide the relay which until the calling-plug is inserted clear in the spring-jack leaves the tip connected to earth through the tertiary of the operators induction-coil, but disconnected from the battery. A test may thus be made with the calling-plug, and after the test the circuit of the conductor 5 is automatically completed by the relay when the plug is inserted clear in.

Having thus described my invention, I claim as new, and desire to secure by Letters Patent, the following:

1. The line-lam p (Z and the supervisory lamp k, and their local circuits connected with the battery I), the local circuit of lamp (Z including resistance e, in combination with the jack (0 having a test-piece a and the corresponding plug f, the tip f of said plug having a connection to the same side of battery I) with which lamp (Z is connected, said tip f and If the tip of the test-piece (b forming the terminals of a shunt 5 about said lamp (Z, whereby in case the tip of the plug touches test-piece a of the jack, there will be no increase of the current from battery I) through said lamp.

2. The combination with a telephone-line extending from a substation to a spring-jack a at a central office, of a plug and plug-circuit for making connection with the line.,. a central battery I), a local circuit 4 from said battery including serially the line-signal lamp d and resistance 0, and means for controlling said circuit, a normally open shunt 7 about said line-lamp, said shunt containinga supervisory lamp h and being closed in registering contacts f a of the plug and spring-jack, the tip f of-the plug forming the terminal of a second normally open shunt of the line-lamp, whereby the current through the lamp is not increased if the tip f of the plug touches the contact a of the jack, as set forth.

3. The combination with telephone-lines each extending from substations to multiple spring-jacks at a central office, of a pair of plugs and a plug-circuit for uniting lines, a

central battery I), a local signal-circuit from said battery including serially a signal d, a resistance 6 and means for controlling the circuit, a normally open shunt associated with each plug, containing a supervisory signal and adapted to be closed about the line-signal of any line in making connection with the spring-jack of that line, in registering coni tacts f a of the plug and spring-jack respectively, the tip of the plug forming the terminal of a normally open shunt of the linelamp d, which shunt is closed when the tip of the plug touches the contact a of the jack, an operators testing apparatus of high resistance,

and an electromagnetic switch normally connecting said testing apparatus with the tip of the calling-plug, and adapted alternatively to disconnect the tip of the plug from the testing apparatus and connect the same with the tip of the answering-plug, whereby the current through the line-lamp d is not materially increased when the tip of either plug touches the contact-piece a of the jack.

4. In a telephone-exchange switchboard, the combination with telephone-lines and the multiple spring-jacks thereof, of a pair of plugs and their plug-circuit for uniting lines, a battery, a local circuit from saidbattery for each line, including serially a line-signal and a resistance, a line-relay having switchcontacts controlling said local circuit, a shuntcircuit containing a supervisory signal associated with each plug, adapted to be closed about the line-signal of any line in plugging into a spring-jack of that line, said shunt being established in registering contacts of the thimble of the jack and the shank of the plug, the tip of the answering-plug of each pair being connected to complete a shunt of the line-signal in touching the thimble of the jack, an operators testing appliance normally connected with the tip of the calling-plug of each pair, and an electromagnetic switch actuated upon the insertion of the calling-plug in a spring-jack, adapted to disconnect the tip of such plug from the testing appliance and connect the same with the tip of the mate plug.

In witness whereof I hereunto subscribe my name this 20th day of November, A. D. 1901,

FRANK R. MCBERTY.

Witnesses:

EDWIN H. SMYTHE, FREDERICK A. WATKINS. 

